Add Missing Includes Across src/libslic3r

Every libslic3r source and header now directly includes the headers declaring what it uses, rather than relying on the precompiled header or transitive includes. Generated with clang-tidy misc-include-cleaner, with libslic3r headers spelled libslic3r/... so they resolve outside the library's private include paths. MultiMaterialSegmentation.hpp, Support/SupportParameters.hpp and Format/STEP.hpp are made self-contained by hand.

src/libslic3r/ExPolygonCollection.hpp

@@ -1,10 +1,13 @@
 #ifndef slic3r_ExPolygonCollection_hpp_
 #define slic3r_ExPolygonCollection_hpp_
 
+#include "Point.hpp"
+#include "Polygon.hpp"
 #include "libslic3r.h"
 #include "ExPolygon.hpp"
 #include "Line.hpp"
 #include "Polyline.hpp"
+#include <vector>
 
 namespace Slic3r {